1. Field of the Invention
The present invention relates to a capacitive semiconductor device for detecting a dynamic quantity as a change of capacitance.
2. Description of the Related Art
A capacitive semiconductor device is used for an acceleration sensor and a yaw rate sensor, for example. A semiconductor acceleration sensor for a vehicle air bag has a stack structure. In the stack structure, a sensor chip having an acceleration detector is mounted on a circuit chip having a signal processing circuit, and the circuit chip is mounted on a package made of a ceramic substrate. Conventionally, a bonding wire is used for electrical connections between the sensor chip and the circuit chip, and between the circuit chip and the package.
Instead of the bonding wire, a bump may be used for the connections between the sensor chip and the circuit chip, and between the circuit chip and the package, as disclosed in US 2004/0173913 A1 (corresponding to JP-A-2004-271312).
For example, as shown in FIG. 10A, a sensor chip 1 is arranged in a face down position against a circuit chip 2, and first electrode pads 1a of the sensor chip 1 are coupled with second electrode pads of the circuit chip 2 through first bumps 3. In this case, four first bumps 3 (electrode pads 1a) arranged at center portions of each side of the sensor chip 1. The circuit chip 2 is arranged in a face down position against a package 4 in a multi-chip module state, and third electrode pads 2a of the circuit chip 2 are coupled with electrode leads through second bumps 5. The electrode leads are disposed at the package 4.
The capacitive semiconductor sensor of US 2004/0173913 A1 is prevented from an affection of a parasitic capacitance at electrical connection parts (bumps 3) between the sensor chip 1 and the circuit chip 2, and a performance is improved. Furthermore, a mounting workability is improved, and a chip design becomes flexible.
However, the sensor chip 1 and the circuit chip 2 are electrically and mechanically coupled through only the four first bumps 3. Thus, the capacitive semiconductor sensor is relatively weak against an impact, thereby when the capacitive semiconductor sensor receives a high impact, the first bumps 3 may be injured.